One of purpose of admin password is to avoid disclose of sensitive part of configuration. If you are responsible admin, you know the password. If you forgotten the password, well, no problem, reset device to factory default, as admin you have all necesarry informations to configure it again.
If you are not responsible admin, you know no password, and you know no configuration details so you can't recreate the configuration from scratch, then the current configuration should not be disclosed to you (because of some sensitive informations from it).
That's all.
If your device is configured to fetch remote provisioning, then modify the provisioning source and change the admin password this way.
If you device is not remote configurable (remote provisioning not configuret or disabled), then device needs to be reset to factory default.
If reset to factory default is disabled, you are out of luck unless responsible administrator will tell you the valid password.
If you device is customized/locked to particular VoIP operator, then you are out of luck even with the reset to factory default. You will not know the operator-customized admin password even after it. In such case, only the VoIP operator in question may help you.
